Make Your Own KK2 LED Alarm

Introduction

When my KK2.1 multi-rotor board arrived from HobbyKing, I was disappointed when I realized it doesn't include the warning LED that they have pictured with the KK2. So I decided to make my own and I'll show you how in this video and article. If you want to quickly see step-by-step instructions, then watch the video or if you prefer reading, then read this article.

HobbyKing sells these, but it turns out you probably already have the things needed to make one yourself.

How the KK2 Alarm Works

The KK2 has the ability to sense your battery voltage. It comes with a little warning buzzer. You set the alarm voltage on the KK2 and when it reaches that voltage the buzzer starts sounding and when it goes below that voltage it sounds more frequently. What happens is the KK2 outputs 5 volts on the 2 pins used for the buzzer. You can use this alarm output for a warning LED also. You can use the buzzer alone, the LED alone or both together. You can even do multiple LEDs. Below is my quad with two LEDs.

The connection the buzzer uses used to be a standard black male servo connector, but with the KK2.1, HobbyKing started using a red male JST connector. If you have the red male JST connector and you want to use more than just a buzzer, I would suggest replacing the JST connector with a servo connector to make connections easier.

Note, make sure you connect your flight battery to the KK2 so that it can sense the voltage. The KK2.1 has a 2-pin header that you can connect a JST or servo connector to. The KK2.0 requires you solder leads onto the KK2 board itself.

Making the LED Alarm

1. Getting a servo lead. We’ll need a male servo connector for the LED. I cut mine off of a bad servo. You can also purchase one if you need to.

Since they both use servo connectors, if you need the alarm output to go to a buzzer and a LED, you just plug both into a servo Y-connector.

2. Choose an LED. You can use just about any LED for this and any color you like. Here are 3 different LEDs from the dimmest to brightest.

I’m going to use these very bright 115 lumen LEDs. This most closely resembles the LED you get from HobbyKing. These are super bright. Here are links to where you can purchase the 3 LEDs:

Standard 5mm LED

SMD LED (can remove these from light strip)

High Power LED

Now a LED typical uses around 3 volts, but remember the alarm output is 5 volts, so if you hook up an LED directly, it’s going to burn out eventually. So to remedy this we just need to add a resistor in our circuit.

3. Choose a resistor. So what kind of resistor do you need? We just plug the numbers into a LED resistor calculator to find out. The source voltage is 5 volts for the KK2. The diode forward voltage from the LED is 3.8V. If you’re not sure, I would use 3.2V. The diode forward current is 350mA. I click “find R” to find the resistance. It says I need a size of 3.9 ohms. You can round up to the next closest resistor if you need to, which for me is 7 ohms.

4. Solder the servo lead, LED and resistor in a circuit. Now it’s just a matter of connecting our servo wire to the resistor and LED in a simple circuit. Here is what it will look like when we are done (shown without heat shrink):

Start by cutting the wire from both sides of the resistor, leaving only 1 cm (3/8"). Pull apart your servo wire and if you want you can either cut or remove the yellow [or lightest colored wire] wire by prying up the tab on the connector and pulling the pin out. We’re only going to use the red and black wires.

Somewhere along the red wire, we want to cut out a space for the resistor. Place the resistor next to it and mark the resistor location and the end of each wire. Our goal is to put a resistor in line here, but keep the red wire the same length as the black wire. The red wire will be positive and the black wire will be negative.

Cut out the black marked area in the middle and strip 1 cm (3/8") on each side so that it looks like this.

Mark the negative and positive pins on the LED with markers. Read this to find out how to tell the difference between positive and negative leads on an LED.

Strip the ends of the servo wires so there is just enough wire to make contact with the LED. Tin all your connections, the wire ends on your servo wire, the resistor ends and the LED leads.

Now we just need to solder the circuit together. Slip a piece of heat shrink over the red wire before starting this step. Solder the separated red wire to the resistor. Solder the resistor to the other red wire. Slide the head shrink over the resistor and heat it. Solder the red wire to the positive LED lead and the black wire too the negative LED lead. If you have long leads you may want to consider using heat shrink.

Here is LED (shown without heat shrink):

Testing the Alarm

Let’s see how this works now. We plug the buzzer and LED into the alarm output on KK2 using the Y connector. I’m actually using 2 LEDs and the buzzer for mine. If I go into the Miscellaneous Settings menu on the KK2, there is a setting called Alarm 1/10 volts.

This tells the KK2 to start triggering the alarm when the voltages goes down that far and the voltage drops lower, it increases in frequency. Now this setting is in 1/10 volts. So 130 means 13.0 volts. In the video, you can see what happens when I set it the alarm to 126 and voltage is a 12.5V. The warning flashes slowly. When you increase the difference in the alarm setting, the warning flashes more frequently. So, essentially you would have more warning as your battery voltage drops lower and lower.